Govindasamy Bala

A lot of people today are talking about offsetting their carbon footprint to prevent global warming, and one way is to plant trees, because trees take up carbon dioxide. But the real role of trees in our climate is the question that we've addressed in our study.

There are people who believe we should plant trees all over Europe and North America to solve the climate change problem. They should know that the only place where planting trees prevents global warming is in the tropics. In the temperate regions it doesn't produce results, and in the high latitudes it's really counterproductive.

Trees have other effects on climate change besides absorbing carbon dioxide. In the tropics, they take up water from the deep soil and release it as vapor in the air. That helps form clouds and reflects sunlight, cooling the surface of the planet. But there's also what we call the "albido effect." In high latitudes, if you don't have trees you have snow-covered areas, and elsewhere rocky desert and grassland.

Those areas reflect as much as 90% of the sun's light, whereas if you planted trees there they would reflect only about 10%. So planting trees in these climates actually has the net effect of warming the Earth's surface. In planning policy, you have to look at all these effects, and that's what our study does.

That doesn't mean we should cut down all the trees in these regions. The whole purpose of protecting climate change is to protect the Earth as a whole. So the real solution is still cutting down fossil fuel emissions and investing in alternative energies. But in the meantime we have these secondary strategies. People still want to emit, and they'll pay for their indulgences.

Govindasamy Bala is a physicist at the University of California's Lawrence Livermore National Laboratory and specializes in climate change.